In a fuel cell stack, a stack is formed by laminating a plurality of fuel cells, each comprising a membrane electrode assembly (MEA) in which an anode electrode and a cathode electrode are respectively joined to either side of an electrolytic membrane. In each of the fuel cells, a fuel gas and an oxidant gas are respectively fed into the anode electrode and the cathode electrode, to thereby cause an electrochemical reaction for generating electric power. During the electrochemical reaction, because thermal energy is also generated in addition to electrical energy, cooling water is passed through a cooling water channel formed between fuel cells which are adjacent to each other, to cool each of the fuel cells.
When each of the fuel cells is cooled, however, there are some fuel cells which are more likely than others to be lowered in temperature by heat dissipation into the outside. For example, in fuel cells located close to an end part in a stack direction of the stack, because a lot of heat is radiated from a terminal electrode (a current collector) for extracting electrical power, an end plate disposed to retain the stacked fuel cells, or the like, the temperature of the fuel cells will be easily lowered. Such fuel cells whose temperature is lowered are prone to formation of condensation due to condensed water vapor, which tends to result in degradation in power generating performance of those fuel cells.
JP 8-306380 A discloses a structure in which a heat insulating barrier or a heater is installed at an end part of a stack in a stack direction. In this Publication of JP H08-306380, the heat insulating barrier or the heater is designed to suppress the lowering of temperature of fuel cells located in the vicinity of the end part of the stack in the stack direction. However, by simply suppressing the lowering of temperature of the fuel cells, it is difficult to realize water vapor being adequately prevented from condensing in the fuel cells, and accordingly preventing degradation of power generating performance of the fuel cell to a sufficient degree.